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Attrition-Induced Spontaneous Chiral Amplification of the Γ Polymorphic Modification of Glycine

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Attrition-Induced Spontaneous Chiral Amplification of the Γ Polymorphic Modification of Glycine CrystEngComm Attrition -induced spontaneous chiral amplification of the γ polymorphic modification of glycine Journal: CrystEngComm Manuscript ID: CE-COM-12-2014-002434.R1 Article Type: Communication Date Submitted by the Author: 03-Jan-2015 Complete List of Authors: Tarasevych, Arkadii; Boreskov Institute of Catalysis, Siberian branch of the Russian Academy of Sciences, ; Institut des Sciences Chimiques de Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS Sorochinsky, Alexander; Institut of Bioorganic Chemistry and Petrochemistry, National Academy of Sciences of Ukraine, Kukhar, Valery; Institute of Bioorganic Chemistry and Petrochemistry, National Academy of Sciences of the Ukraine, Toupet, loïc; Université de Rennes 1, Institut de Physique de Rennes Crassous, Jeanne; CNRS-Universite de Rennes 1, Sciences Chimiques de Rennes Guillemin, Jean-Claude; Institut des Sciences Chimiques de Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS Page 1 of 10CrystEngComm CrystEngComm Dynamic Article Links ► Cite this: DOI: 10.1039/c0xx00000x www.rsc.org/xxxxxx ARTICLE TYPE Attrition-induced spontaneous chiral amplification of the γ polymorphic modification of glycine Arkadii V. Tarasevych,* a,b,c Alexander E. Sorochinsky,b Valery P. Kukhar,b Loïc Toupet,d Jeanne Crassous,* d and Jean-Claude Guillemin*a 5 Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX DOI: 10.1039/b000000x Glycine is the simplest achiral amino acid that undergoes the α-carbon and, as a consequence, is achiral. In the crystalline spontaneous mirror symmetry breaking when it crystallizes state it can exist in several polymorph modifications: α, β and γ 11 in its chiral γ-polymorphic modification. As a result of 50 under ambient conditions and β', δ, ε and ζ under high pressure. 10 Ostwald ripening, its racemic mixture stochastically becomes Among them γ polymorphic modification crystallizes in optically active. The sense of the resulting handedness can be enantiotopic space groups P31 and P32. In spite of the numerous controlled by addition of one enantiomer of a simple chiral studies in crystallography devoted to the different aspects of amino acid, the alanine. glycine modifications including recent single crystal analysis of 55 its gamma form and correlation between its absolute structure and 12 Introduction optical rotation, no attempts have been done to achieve its homochirality . Moreover it has been reported that γ-Gly is a very 15 Proteinogenic chiral amino-acids all possess the L configuration promising material for non-linear optical (for second harmonic and this single handedness is considered as the hallmark of the generation) and piezoelectric applications; its mixed crystals 13 living world (homochirality). Among the plausible explanations 60 revealed ferroelectric properties. Here we study spontaneous for the origin of such homochirality is the formation of a slight and induced increases of optical activity in the γ-Gly crystalline enantiomeric excess that may be increased by an amplification phase using solid state circular dichroism. 1a 20 process. Stochastic “mirror-symmetry breaking” that may occur during a crystallization process is among the possibilities for the Results and discussion emergence of a chiral bias in the statistical distribution of optical isomers. 1b γ-Gly was obtained according to the described method of Crystallization-induced asymmetric transformations of chiral 65 Srinivasan et al. through its crystallization from an aqueous sodium chloride solution (see ESI). 14 The crystal structure of γ 25 organic compounds are among the most appealing methodologies for getting pure enantiomers from racemates or scalemic polymorphic modification has been confirmed by powder X-ray mixtures. 2,3 More particularly, asymmetric transformations of diffraction (see Figure S1). In the recent paper of Chongprasert et 11b interconvertible enantiomers forming conglomerates can al. it was demonstrated that depending on the conditions theoretically provide 100% yield of the desired enantiomer. 70 (temperature, concentration, rate of cooling and crystallization), the crystallization of aqueous solutions of glycine can provide 30 Beside the asymmetric transformations of chiral interconverting molecules, 4-6 the phenomenon of spontaneous mirror symmetry any of its three modifications ( α, β, γ) or a mixture of them. The breaking in chiral crystals of achiral substances can be thermodynamic stability of these forms is decreasing in the order 11b encountered, such as for example in the striking and intensively γ > α > β, however during crystallization from aqueous studied crystallization of sodium chlorate and bromate, 7 for 75 solutions its α modification forms faster. In the initial experiments our goal was to determine the 35 which the attrition-induced spontaneous chiral amplification (AISCA) phenomenon has been demonstrated. 10 The process of specific value of circular dichroism (CD) in the solid state. matter exchange between two phases leading to the loss of During the slow crystallization of glycine from NaCl solution asymmetry in one of the phases can be regarded as racemization. without stirring, the majority of obtained single crystals revealed The mechanism of spontaneous chiral amplification involves (i) 80 CD signal around 210 nm with random distribution of levo and dextrorotary forms while the whole crop had no optical activity 40 interconversion between antipodal crystals due to the equilibrium with the liquid phase, alongside with (ii) so-called Ostwald (Table S1, entries 1-7). This result agrees well with former 6c,7a,7c,7f,8 ripening in the solid phase (growing of larger crystals at the studies. expense of smaller ones). The autocatalytic enantioselective It is noticeable that the specific ellipticity (mdeg/mg) changed nucleation leads to the gradual evolution of the crystal optical 85 its absolute value from crystal to crystal under the same conditions of measurements (entries 2-7). Some of crystals had 45 purity up to the homochiral state. Glycine is the simplest amino acid which, in contrast to all zero CD signal (entry 1). The highest values of CD signals other proteinogenic amino acids, does not contain substituent at obtained for individual crystals reached |40.2| mdeg/mg (entry 6). This journal is © The Royal Society of Chemistry [year] [journal] , [year], [vol] , 00–00 | 1 CrystEngComm Page 2 of 10 Presumably, the inconstancy of the CD signals can be caused by (Figure 3, CD bands in color). A sharp rise of the optical activity rd the epitaxial nature of γ-Gly conglomerate, namely by 60 was observed on the 3 day of grinding and made eventually up simultaneous presence within individual crystals of enantiopure to about 70 mdeg/mg (Table S1, entry 19). We supposed that the domains of both enantiomorphous l and d forms grown together. final value of CD signal corresponds (or at least is very close) to 5 On the other hand, several years ago Ishikawa et al. reported that the 100% of the enantiomorphous excess.‡ The Figure 3 (the besides optically active crystals, γ-Gly can form monohedral negative CD bands) represents the evolution of homochirality 12 twinning form. An attempt of distinguishing between levo 65 during 9 days. The analysis of the obtained data in the and dextrorotary crystals of γ-Gly visually using a polarizing coordinates “time – specific ellipticity” (at a selected wavelength microscope failed. Furthermore, X-ray crystallographic studies on ~210 nm) gave a curve of the sigmoidal shape which is very close 10 a micro-source Cu diffractometer of several selected single to the Bolzmann type (Figure S2), that points out the pronounced crystals obtained under these conditions all displayed the P31 autocatalytic character of the process of evolution of single space group (see ESI). 70 handedness. Our further experiments on the crystallization of γ-Gly were In the next 3 independent ripening experiments using glass conducted under intensive stirring of the solution (see Table S1, beads starting from the same optically inactive material we 15 entries 8-18). Figure 1 represents the results of 11 independent confirmed the stochastic behavior of the asymmetric crystallizations. In 4 experiments we observed the formation of amplification (Figure 3, black dotted curves, Table S1: entries 20- nd levorotary form of γ-Gly (Table S1, entries 8 and 14-16); 6 75 22). The grinding was stopped on the 2 day for CD crystallizations shown positive CD signals (entries 9-13 and 18) measurements. Although the experiments were conducted under and one of the 11 crops virtually had no optical activity (entry similar conditions, the resulted optical activity was different: one 20 17). of the mixtures had been virtually unchanged (entry 22) and 2 The distribution histogram (Figure 2) of the specific others revealed some positive CD signals (entries 20-21). ellipticities for the crops obtained under intensive stirring (Figure 80 Finally we demonstrated the possibility to control the 1, see also ESI, Table S1, entries 8-18) corresponds to a feebly handedness of the obtained γ-Gly by means of addition of small marked bimodal symmetrical distribution centered at 0° and amounts (5% by weight) of enantiopure L and D alanine under 25 having two peaks around ±3 mdeg/mg. Similar distribution shape the conditions of intensive stirring with glass beads. Figure 4 has been observed by Kondepudi et al. in 10 independent represents the results of the asymmetric induction: the spectra of 8 crystallizations of 4,4'-dimethylchalcone under intensive stirring. 85 enantiopure L-Ala (dotted curve) and its mixtures with γ-Gly in Kaptein et al. demonstrated the possibility of deracemization of the course of the crystal enantiomorphic excess evolution are an epitaxial racemate. 4 Obviously in our case better fitting the drawn in red; the corresponding negative CD-active band 30 conditions for the chiral ripening of the solid phase (temperature, centered around 210 nm induced by D-Ala are in blue; the time, and intensity of crushing of crystals) might lead to a more spectrum of the optically inactive γ-glycine which was used for pronounced bimodal shape of the histogram. 90 the experiments is in black.
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